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Ampney Brook upstream before pipe_edited

Investigating the health of our rivers

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We used Environment Information Regulation requests to gain access to industry data. The data on this page has been provided by the Environment Agency and Thames Water. Analysis has been conducted by Professor Peter Hammond. 

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Sewage can be legally discharged into rivers

Excess sewage discharges can be permitted in exceptional circumstances, ‘such as unusually heavy rainfall’. Even then, it must be treated to certain standards.

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The Environment Agency may record fewer than 3.5% of
Thames Water's unpermitted spills*

Our analysis shows that many unpermitted spills go undetected by the Environment Agency. This is partially because they only request daily data from Thames Water. We request data recorded at 15 minute intervals - giving us a more detailed picture.

* Our analysis suggests there were 944 spills between 2010 & 2020 from Thames Water sites that breached permitted treatment standards. The Environment Agency records only list 33.

How bad is sewage pollution near you?

The Cotswolds

MP: Sir Geoffrey Clifton-Brown

 12th worst 
 sewage spillers in England 
 

12th worst out of 533 constituencies,
based on 2019 data

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Time spent spilling sewage into Cotswold waterways: 10,086 hours

MP: Robert Courts

 6th worst 
 sewage spillers in England 
 

6th worst out of 533 constituencies,
based on 2019 data

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Time spent spilling sewage into Witney County waterways: 13,295 hours

Witney County

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Sewage is spilling into our rivers more frequently every year

Number of days when sewage was spilled that didn't meet minimum treatment standards.png

The number of days when sewage was spilled that didn't meet minimum treatment standards

Data source: Thames Water

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Let's look up close at two sewage works

South Leigh

Sewage Treatment Works

 3342 hours 
 spent spilling sewage 
 

Thames Water data
1 Jan - 31 Dec 2020

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Sewage is spilled into Limb Brook

Sewage Treatment Works

 2484 hours 
 spent spilling sewage 
 

Thames Water data

1 Jan - 31 Dec 2020

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Sewage is spilled into

Harcourt and Chil Brooks

Stanton Harcourt

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Sewage spills last for months

The blue line shows when untreated sewage was spilled. You can see that it's happening for months on end.

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Data source: Thames Water

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Environment Agency classification of Chil and Limb Brooks

This has a devastating effect on local brooks

The Chil and Limb Brooks have changed hugely since 2012. This is the cumulative effect of Thames Water spilling untreated sewage into their waters.

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It's already too late for some of our wildlife

Every spring, wildlife tries to bounce back from a winter of pollution. But eventually it will be unable to recover. We may have already lost the rare filter feeders, called Crystal Moss Animals, which once lived in Chil Brook.

A small colony of Bryozoan Lophopus, also known as Crystal Moss Animal
© www.micrographia.com

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We want our river back

Further data analysis

An in-depth review of unpermitted spills from sewage treatment works

Report: part one

We investigated 14 sewage treatment works in West Oxfordshire and the Cotswolds – all owned by Thames Water.

Report: part two

We analysed data from 58 sewage treatment works. They're broadly representative of sewage works across England and Wales.

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Using machine learning to detect untreated sewage spills

Image by Carlos Muza

We present a new way of identifying likely sewage spills. Using machine learning, known spill events served as training data. The probability of correctly classifying a randomly selected pair of ‘spill’ and ‘no-spill’ effluent patterns was above 96%.

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